Basic Temperature Physics of Radiantly Heated
Balls

It is commonly asserted
that the basic physics of planetary temperature is well understood.
However, it is surprisingly difficult to find any exposition of that
basic physics. This lack contributes to the most egregious
impossibilities being touted as ultimate horrors we might face if we
don't mend our ways. On the skeptic side, it has even been claimed that
the notion of a planetary mean is meaningless. I
present below my current understanding. I welcome review and, indeed,
co-authorship with someone with more established credentials.

I originally started
working on this
around Thanksgiving 2008 and hoped to propose talking about it at the Heartland Institute's
March 2009 climate conference , but clearly , it's too late for that .
I find that altho my master's thesis had integrals which filled a page
, having spent an adulthood in the arrays of the most powerful
languages for modeling actual finite data , I'm terminally inept at
expressing ideas in traditional maths notation . I have , however ,
instantiated the basic formulas for anisotropically irradiated
anisotropically shaded gray balls in the rather obscure APL
evolute K. I believe , tho , that the succinct model can be
understood and
translated into common array capable languages by anyone
familiar
with any such language . (
seeForumfor translations to J and Dyalog
APL . )

I will not consider fluid motion of
the atmosphere because our interest is with mean temperature averaged
over the sphere over time. Our
interest is in the constraints on the temperature of radiantly heated
balls like our earth, in a sense looking from the outside rather than
looking up at the complexities of the atmosphere.

The fundamental law whose most
superficial application explains all but at most a couple of percent of
the earth's temperature is the Stefan-Boltzmann law. Applying this
basic law for black bodies to the surface temperature of the sun and
the solid angle it makes in the sky explains the mean temperatures of
each of the inner planets, except for Venus, quite closely as shown in
the graph [0] .

The Stefan-Boltzmann law
is a simple equation
with a complicated constant derived from fundamentals which states that
the Power radiated by a body is its Emissivity
times the stefan-boltzmann
constant times its Temperature
raised to the 4th power.

The "Black
Body" Wikipedia page was the first place I saw the derivation
of the Earth's temperature from the Sun's based on this equation. It
simply equates the power radiated by the sun and intercepted by the
disk of the earth with the power radiated by the earth in all
directions:[1]

( ( pi
* Re ^ 2 )

*

( sb
* Ts ^ 4 )

*

( 4 * pi
* Rs ^ 2 )

%

( 4 *
pi
* D ^ 2 ) )

area of earth facing
sun

*

radiance of sun

*

surface area of sun

%

area of earth
orbit
sphere

=

( ( 4
pi *
Re ^ 2 )

*

( sb
* Te ^ 4 ) )

|
e1 |

surface area
of earth

*

radiance of
earth

Canceling terms and rearranging a
little, we get

( ( Ts ^ 4 ) * ( Rs ^ 2 ) % ( 4 * D ^ 2 ) ) = (
Te ^ 4 ) | e2 |

and taking 4th roots:

Te = ( ( Rs % 2 * D ) ^ % 2 ) * Ts | e3 |

or to express as a function :

Trd : {[ R ; D ] ( ( R % D ) % 2 ) ^ % 2
} | e4 |

Note that the radius of the Earth has
dropped out; thus a point is equivalent to a sphere, and only the solid
angle subtended by the Sun matters.

Plugging in values of 6.96e8 and 1.496e11 meters
for the radius of the
Sun and the distance from the Earth to the Sun gives the result th at
the temperature of a black body in Earth's orbit has a
temperature of about 0.04823 the surface temperature of the Sun . This
is the computation which produces the green line in the plot above.

Note that given that the SolidAngle
subtended by the a disk of radius R at distance D
is

( %/ ; -/ ) .\: r 1 0 />/ 1.016852 4.657602
/ the quotient and difference of the ap- and peri-helion
temps
in the last result .
/ This > 1% difference between
ap- and peri-helion temps should be easy to confirm .

Gray Bodies

But, of course, the real planets are
not black. For a "gray" body, there is an associated parameter Emissivity,
constant across the spectrum, which like a gray filter in front of a
radiating black body, uniformly reduces the power at each frequency
from what would be expected from a black body. There is a complementary
parameter Absorptivity, ranging from black to
totally reflective, which quantifies the tendency of a substance to
absorb radiant energy.

150 years ago in 1859, Gustav
Kirchhoff realized that at equilibrium, the emissivity of an object
must equal its absorptivity, E = A . Thus equation e2
above would become

with terms Ae *
and Ee * added to the left and right sides for the Absorptivity
and Emissivity of the earth
respectively. But, by Kirchoff, these terms cancel out at equilibrium.[2] In the middle of 2008, the Wikipedia
Black Body page was modified adding the Ae to the
left side of this equation but failing to add Ee to
the right side.

The most common explanation of the need for a
"greenhouse" effect is that because the reflectivity, ( 1 -
Ae ) , or albedo ( unfortunately
also beginning with "A" ) of the earth is about
0.3, and therefore its absorptivity about 0.7 , its mean temperature
should be only about the 4th root of 0.7 , or about 0.91 the
temperature calculated above. The approximately 30c difference between
this value and the earth's actual temperature which is quite near the black
body value is asserted to be due to the effect of the "greenhouse"
gases. Thus the putative greenhouse effect is
not explained thru
explicit quantitative physical assertions, rather simply an assertion
of the need to fill a gap created by an incorrect equation.

Judging from Wikipedia references,
this explanation of the greenhouse effect seems to be common in texts
on global warming. But this explanation is simply wrong. If it were the
case, one would expect a ball coated with Magnesium Oxide with an
albedo of about 0.9 to come to an equilibrium temperature of about
-120c in a vacuum bottle sitting in room temperature surroundings.
Venus has the highest reflectivity of all the inner planets, about 0.75
. This would imply a temperature about 30% below the
calculated black body temperature for its orbit, or about 233k
versus 328k . However, of course, Venus is radiating energy at a
temperature of about 735k, both on the side facing and away from the
Sun -- and its day is slightly longer than its year. The most heating
this greenhouse theory could predict is raising the temperature back to
the black body temperature. No "runaway" effect could raise the
temperature beyond that. On the other hand, according to this theory,
as snow with an albedo which can be nearly as high as MgO covered the
continents during the ice ages, the Earth should have spiraled down to
a permanent snowball. That it didn't is one of the first facts which
made me question the AGW orthodoxy. It is notable that, so far as I
know, there is no laboratory demonstration of this supposed
phenomenon.

From
this point on , I will use actual expressions from my K implementation
of the Stefan-Boltzmann Law for the simple case of a point in its
surrounding sphere .The equilibrium
temperature of a
ball will vary
if the absorptivity/emissivity parameter is different in
directions with different temperatures. We can express this
as a function on 3 vectors and a scalar : a partition of the celestial
sphere, SfeerPart , the temperature of each
partition of the celestial sphere , Tcs , the
absorptivity/emissivity of each partitian , AE ,
and the temperature of the ball considered to be uniform , Tp
.
( This is the parameter upon which it is a point . ) We will just deal
with a partition of the sphere into ( SunDisk ; DaySide ;
NightSide ) .

Other than the disk of the sun , the celestial
sphere presents the approximately 3 degree K microwave background
radiation . We'll include it altho taken to the 4th power it ends up
being quite negligable .

Finally , there is the
absorptivity/emissivity , the grayness , of each sphere partition . We
will look at several cases starting with all black .

: AE : 1 1 1
/>/ 1 1 1

(
SfeerPart ; Tcs ; AE )
/ Here's a summary table .

5.4113742e-006

5778

1

0.49999459

3

1

0.5

3

1

Total radiated
power from shaded gray ball

/ Multiplying the "grayness" , portion of the sphere , and
power for the celestial
/ sphere and "earth" at 279K give the following numbers for each part
of the sky . { AE *
SfeerPart * Psb x } @/: ( Tcs ; 279 ) / "@/:"
applies its left on each right .

We can use K's secant
descent search function to find the point temperature balancing its
surrounding sphere temperature distribution by searching for a
difference of 0. K's "?"
function takes a third argument which
is a starting guess to keep the aritmetic computable .
300 will work here .

?[ Tdif ; 0.0 ; 300 ] />/ 278.67912

Note that this matches the 278.6791 obtained
for a solar temperature of 5778K using Trd above .

Confirming that Venus is much hotter than any simply radiantly heated
object in its orbit could be . There must be some other internal source
of heat . ( Note in comparison that the atmosphere of
Mars is 95% CO2 yet its temperature matchs the S-B&K
calculation . )

I do not understand how James Hansen could possibly have claimed that
Venus's mean temperature could be due to heat trapping of any sort . I
understand even less how such claims could have survived the most
cursory "peer" review .

To complete the analysis for colored bodies , the spectrum needs to be
"unfolded" like direction has here . Then , the effect of the couple of
notches in CO2's specturm can be calculated . A priori , the specturm
representing only about .08 of the sun's , and already rather saturated
at levels at which plants barely survive , the effect on mean
temperature is likely to be de minimis . The effect on reducing diurnal
variance , tho , ought be calculated .

[1] My notation is informed by an
adulthood living in APL
languages. The rational is summarized here
. Perhaps the only non obvious symbol is %
for division and reciprocal. In
APL languages f/ can be read as "f across",
for instance +/ is "sum". "

[2] I've heard complaints that the Earth
and Sun are not in equilibrium, but I believe that over a cycle, like
Earth's yearly cycle, it can be proved that for a conservative quantity
like energy, the outcome is equivalent.
I have seen it pointed out that Kirchhoff's equating of absorption and
emission only applies at equilibrium. However absorption and emission
spectra are generally rather constant for a substance over a given
physical state. For instance, it is when water changes to snow that
it's albedo changes drastically.

This Wikipedia section has been
screwed up by the introduction of a term for absorptivity of the earth
without the countervailing term for emissivity in the expression for
radiation from the earth.